The present invention relates to apparatus and methods for preventing freezing of wellhead equipment associated with gas wells and oil wells. More particularly, the invention relates to such apparatus and methods that utilize heat from flameless heat sources such as infrared heaters.
Freezing of wellhead equipment is a common risk for oil wells and gas wells in regions that experience extremely cold winters, such as Alaska and northern Canada. Natural gas contains hydrates, which may condense out of the gas and then solidify when temperatures are very low, particularly when the situation is aggravated by a drop in gas pressure. Unless sufficient heat is provided, or unless other means are provided for preventing condensation of hydrates, the wellhead equipment installed on a producing well to control and regulate flow of oil or gas, as the case may be, can xe2x80x9cfreeze offxe2x80x9d and cease to function when temperatures fall below freezing (i.e., zero degrees Celsius). When this happens, valuable production is lost, and additional expense must be incurred to have skilled technicians attend at the well site to remedy the freeze-off and restore flow from the well.
The prior art discloses several approaches to the prevention of wellhead freezing, often involving the application of known heat tracing methods. Canadian Patent No. 1,299,620, issued to Anderson on Apr. 29, 1992 (similar to U.S. Pat. No. 5,049,724, issued to Anderson on Sep. 17, 1991), describes a flexible, insulated jacket adapted to fit closely around a specific piece of wellhead equipment. Heat is delivered to the wellhead equipment by means of electric heating cables disposed in a selected pattern within the jacket, and connected to an external electrical power source. Although the Anderson apparatus may function adequately to prevent freezing of the equipment, it has significant disadvantages. Firstly, it must be custom-fabricated to suit particular equipment, and thus is not readily adaptable for effective or efficient use with other equipment. Secondly, it requires an external electrical power source, which may be practically unfeasible or prohibitively expensive, particularly at remote well sites, where the only practicable way of providing electrical power source might be by use of a generator requiring a reliable supply of refined fuel such as diesel oil.
U.S. Pat. No. 6,032,732, issued to Yewell on Mar. 7, 2000, discloses a wellhead heating system that circulates heated coolant, from a liquid-cooled engine driving an oil well pumper, through insulated conduit arranged as desired in thermal contact with the wellhead equipment, such that heat from the circulating coolant is transferred to the equipment. The Yewell apparatus has a serious drawback, however, in that it is applicable only at well sites where a source of heated fluid is readily available, such as where a liquid-cooled engine has been provided for one reason or another.
Other approaches to the problem have included provision of heat tracing loops circulating hot water or steam from heaters or boilers, or direct injection of antifreeze fluids such as methanol. Once again, such approaches are excessively expensive if not entirely impractical for remote well sites, because of the cost and inconvenience of maintaining a reliable source of power or fuel for the heaters or boilers, or providing injection pumps and sufficient supplies of antifreeze fluids. In fact, well-operating companies may find it less costly overall to incur occasional production losses from wellhead freeze-off at remote well locations, plus the expense of sending technicians out to remedy freeze-off situations, than to provide means for keeping the remote wellheads warm, given the cost of providing heat sources (e.g., electric power, diesel generators, or propane heaters) or antifreeze injection equipment needed to prevent freeze-off.
It is commonly necessary to provide an enclosure in the general vicinity of a wellhead to house accessory equipment, such as meters or compressors, which must be maintained above particular temperatures in order to remain functional. These enclosures are often heated using flameless infrared catalytic heaters. Such heaters may be fuelled by propane, although that requires provision of a suitable source of propane at or near the well site. More conveniently and more economically, it is often feasible to fuel these heaters with natural gas diverted directly from the well. The gas may be purified if necessary or desired, using fuel gas scrubbers installed upstream of the heaters, in order to enhance the heaters"" operational efficiency and reliability. By using natural gas directly from the well, these heaters are able to keep the accessory equipment warm without the need for additional sources of fuel or electrical power. Accordingly, infrared catalytic heaters fuelled by natural gas are particularly well suited for use at remote well sites where provision of other fuels or electrical power may be problematic.
Whether fuelled by natural gas or other fuels, however, such heaters are not always used as effectively or efficiently as possible. A heater in a given equipment enclosure will commonly generate more heat than needed to keep the equipment in the enclosure at the desired temperature. It is therefore desirable to make use of this excess heating capacity, which would otherwise be wasted or not optimally exploited.
For the foregoing reasons, there is a need in the oil and gas industry for improved apparatus and methods for preventing freezing of wellhead equipment associated with gas wells and oil wells. In particular, there is a need for such apparatus and methods that minimize or eliminate the need for antifreeze injection, or for supplementary power or fuel. There is a further need for such apparatus and methods that utilize heat from flameless heat sources such as infrared catalytic heaters. The present invention is directed to these needs.
In general terms, the present invention provides an apparatus and method utilizing heat from a flameless heater to heat a fluid that may be circulated through a conduit loop, a portion of which is deployed sufficiently close to an object desired to be heated, such that the heat from the fluid is transferred to that object, thereby heating it. The conduit loop may also be referred to as a heat tracing loop, the phrase xe2x80x9cheat tracingxe2x80x9d being commonly used to refer to any method that deploys heating elements (which may include electrical heating cables or, as in the present case, conduit carrying a heated fluid) in close association with an object to be heated, such as a piece of equipment or a length of piping.
In the present invention, a heat exchanger filled with fluid is placed in close proximity to the heating element of a flameless heater, such as an infrared catalytic gas heater, such that heat from the heater is transferred to the fluid in the heat exchanger. The heat exchanger has a filler opening to be used for introducing a fluid into the fluid reservoir. It also has a fluid inlet and a fluid outlet, both of which are in fluid communication with the fluid reservoir. The conduit loop is connected at one end to the fluid inlet and at the other end to the fluid outlet, and loop may be considered as comprising two sections, namely a supply section originating at the fluid outlet, and a return section terminating at the fluid inlet. The supply section and the return section are essentially contiguous, the point of demarcation between them being the region where, in a given application, the fluid begins to flow back to the heat exchanger rather than outward therefrom. A pump, such as an electric or gas-actuated pump, is provided for circulating the heated fluid through the conduit loop.
Accordingly, in one aspect the present invention is a heating apparatus, for use in association with a flameless heater having a heat-radiating element, said apparatus comprising:
a heat exchanger having an interior reservoir, a filler opening, a fluid outlet, and a fluid inlet;
a conduit loop running from the fluid outlet to the fluid inlet, said conduit loop comprising a supply section originating at and connecting to the fluid outlet, and a return section terminating at and connecting to the fluid inlet; and
a pump associated with the conduit loop;
wherein the heat exchanger is positioned sufficiently close to the heat-radiating element such that a fluid within the interior reservoir may be heated by radiant heat from the flameless heater.
In another aspect, the invention is a heating apparatus comprising:
a flameless heater having a heat-radiating element;
a heat exchanger having an interior reservoir, a filler opening, a fluid outlet, and a fluid inlet;
a conduit loop running from the fluid outlet to the fluid inlet, said conduit loop comprising a supply section originating at and connecting to the fluid outlet, and a return section terminating at and connecting to the fluid inlet; and
a pump associated with the conduit loop;
wherein:
the heat exchanger is positioned sufficiently close to the heat-radiating element such that a fluid within the interior reservoir may be heated by radiant heat from the flameless heater; and
the conduit loop is deployed in thermal contact with an object to be heated.
In a further aspect, the present invention is a method for heating a stationary object, said method comprising the steps of:
providing a flameless heater having a heat-radiating element;
providing a heat exchanger having an interior reservoir, a filler opening, a fluid outlet, and a fluid inlet;
providing a conduit loop running from the fluid outlet to the fluid inlet, said conduit loop comprising a supply section originating at and connecting to the fluid outlet, and a return section terminating at and connecting to the fluid inlet;
providing a pump associated with the conduit loop;
deploying the conduit loop in thermal contact with an object to be heated;
introducing a quantity of fluid into the interior reservoir of the heat exchanger through the filler opening;
positioning the heat exchanger sufficiently close to the heat-radiating element such that the fluid within the interior reservoir may be heated by radiant heat from the flameless heater;
activating the flameless heater; and
activating the pump.
In a still further aspect, the invention is a method for heating a stationary liquid-cooled engine, said engine having an internal coolant chamber, a coolant inlet, and a coolant outlet, said method comprising the steps of:
providing a flameless heater having a heat-radiating element;
providing a heat exchanger having an interior reservoir, a filler opening, a fluid outlet, and a fluid inlet;
providing a conduit loop comprising a supply section running from the fluid outlet of the heat exchanger to the coolant inlet of the engine, and a return section running from the coolant outlet of the engine to the fluid inlet of the heat exchanger;
providing a pump connected into the conduit loop;
introducing a quantity of fluid into the interior reservoir of the heat exchanger through the filler opening;
positioning the heat exchanger sufficiently close to the heat-radiating element such that the fluid within the interior reservoir may be heated by radiant heat from the flameless heater;
activating the flameless heater; and
activating the pump.
In the preferred embodiments of the invention, the flameless heater is an infrared catalytic heater fuelled by a gaseous fuel, preferably natural gas. In an alternative embodiment, a second flameless heater is provided, such that the heat exchanger may be xe2x80x9csandwichedxe2x80x9d between the two heaters, thus providing additional input of heat to the fluid in the reservoir.
The heat exchanger may be a simple tank, but it will preferably be a finned radiator in the nature of an automotive radiator, having a fluid reservoir and a number of finned tubes in fluid communication with the fluid reservoir. The fluid used in the heat exchanger may be any fluid suitable for use in a fluid heat-exchanging system, such as water or ethylene glycol anti-freeze fluid. In the preferred embodiment, the apparatus includes a surge tank in fluid communication with the interior reservoir of the heat exchanger. The surge tank allows for expansion of the fluid as it is heated, thereby preventing the development of undesirable pressure build-up within the heat exchanger and the conduit loop.
In the preferred embodiment, a portion of the conduit loop is covered with thermal insulation to minimize loss of heat from the fluid therein, in order to maximize the heat available for transfer to the equipment or other object to be heated.
Where the pump is an electric pump, it may be powered by electricity from an external supply such as conventional electrical service, if available, or an electrical generator. The generator could be a diesel-fired generator, or it could be fuelled by propane or natural gas. In an alternative embodiment, the electric pump is powered by electricity from a storage battery. A solar panel may be provided for generating electricity for storage in the battery.
In the preferred embodiment, the heat exchanger is provided with brackets by use of which the heat exchanger may be conveniently mounted onto the flameless heater in a desirable configuration.
In one embodiment, a shroud is provided for enclosing the flameless heater and the heat exchanger to protect them from the elements in applications where the flameless heater is not situated inside an enclosure.
In a yet further aspect, the present invention is a gas supply system, for use in association with a heating system having a heating exchanger for heating a fluid, a gas-fired flameless heater for radiantly heating the fluid in the heat exchanger, and a gas-driven pump for circulating the fluid from the heat exchanger, said pump having a gas inlet port and a gas exhaust port; said gas supply system comprising:
a primary gas line in fluid communication with the gas inlet port of the pump, for delivering pressurized gas from a main gas supply for driving the pump;
a secondary gas line in fluid communication with the gas exhaust port of the pump, for carrying exhaust gas from the pump to the flameless heater;
a back-up fuel gas supply line in fluid communication with the secondary gas line;
a valve mounted in the back-up fuel gas supply line; and
valve-actuating means, for opening or closing the valve.